I don't have a head kit (it's all standard-40mm) so can't just look into the barrel and at a degree wheel and see where the ports open, but worked out all the spec using CAD. I know the piston position relative to the bottom of the exhaust port, i know the stroke (32mm) , sqiush (0.9mm) and con-rod lenght so can work out the rest from there.
I'm not at work now but if i remember right - my engine, as it came out the box, had 130mm2 transfer area and 190mm2 of exhaust.
Exhaust opened at 108 degrees ATDC
Tranfers opened at 130 degrees ATDC
So blow down (time for exhaust gasses to escape before the tranfers open) was only 22 Degrees!
A good general guide for exhaust, transfer and blow down timing is (plus or minus 5 degrees):
Exhaust= 90 degrees ATDC
transfers= 120 degerees ATDC
Blow down 25-30 degrees ADTC
So my engine standard the exhaust opens nearly 20 degrees to late! has too low a blow down time, and the transfers aren't open long enough buy approx 20 degrees (duration).
It really is quite a poor spec!
On a engine such as the cags where the stroke is only 32mm 2 degrees on the crank equates only to about 0.4mm of stroke! so if you're messing with your timing - you have to do it accurately! E.g. If you raise the roof of any port by only 0.5mm you are changing the timing by approx 3-6 degrees, which is a lot!
I'm fortuate that I am a Toolmaker for a large company so have access to cutting edge machines
I can machine in the ports to the nearest micron (1000th of a millimeter!) which is nice. I'll post some pics of the process as i do it for anyone who's interested.